Cell to cell communication in plants is poorly defined, yet is the key to understanding plant development. The proposed experiments utilize existing and proposed Arabidopsis gene trap lines to define the role of diffusible proteins in both long and short distance signalling during plant development. Functional compartments within the plant will be defined by the characterization of large number of gene trap expression patterns. Proteins involved in short-range apoplastic communication will be identified using a novel genetic screen which identifies secreted or membrane-associated proteins involved in cell communication and identity. New transposon- based gene and enhancer traps will be produced which allow the assessment of reporter gene expression and fusion protein properties in living cells using GFP. The movement of regulatory proteins in the phloem will be investigated by grafting experiments using existing gene trap lines. The knowledge gained from the proposed experiments has the potential to identify basal mechanisms of cell to cell communication in plants, which could lead to insights into development and disease in animals.